Polythiol compounds and resins are well known in art and have found applications as curing agents for epoxies, isocyanates and in thiol-ene chemical reactions. They also have found uses as additives in the rubber industry. Most polythiol curing agents are unpleasant to use because of the residual odor due to impurities and degradation products. Furthermore, most polythiol-cured epoxies cure to give products of low Young's modulus and high water uptake. Examples of commercially available polythiols are shown in FIG. 1.
When used to cure epoxies resins, polythiols have certain advantages over other curing agents such as polyamines because the cure kinetics of epoxies with polythiols is typically more easily controlled than that of epoxies with amines. The time required to reach full hardness can be shortened by increasing the catalyst load while still maintaining a sufficiently long pot-life. The epoxy/thiol reaction often exhibits an induction period during which the mixture of Parts A (epoxy resin) and B (hardener) remains fluid and workable followed by a sharp gelation period when curing commences with rapid development of the final mechanical properties. Thus, the cure kinetics of epoxy with thiol is often non-linear with time, beginning very slowly and then dramatically accelerating at a certain point in time (acceleration point). The acceleration point in a given system may be controlled by choice of catalyst and catalyst loading. Thus, thiol-cured epoxy resins can exhibit a much sharper gel transition than most of the other classes of epoxy hardeners especially at ambient and low temperatures. The initial low-viscosity phase of curing is often called the “application life” and is important in commercial applications to allow sufficient time to apply, cast and tool the product prior to the onset of gelation and hardening. Thiol-curing of epoxies is especially useful for curing at around ambient temperature (4-40° C.) and even at cold temperatures (−30-4° C.).
Curing of epoxy formulations with polythiol hardeners has been described for example by Harris (U.S. Pat. No. 4,092,293, 1978), Johnson (U.S. Pat. No. 4,879,414, 1989 and U.S. Pat. No. 4,927,902, 1990), Motomura (U.S. Pat. No. 4,626,562, 1986), Abbey (U.S. Pat. No. 5,972,423, 1999 and 6153719, 2000), Sakata (U.S. Pat. No. 5,430,112, 1995), Setiabudi (U.S. Pat. No. 5,214,098, 1993), Carr (U.S. Pat. No. 4,177,173, 1979), and Burns (U.S. Pat. No. 6,872,762 B2, 2005).
U.S. Pat. No. 4,092,293 relates to certain propoxylated ether polythiol curing agents for epoxy resins which are reported to impart hydrophobic characteristics to resultant thermoset polymers. This reference is incorporated by reference herein in its entirety for descriptions of epoxy resins, certain useful polythiol curing agents as well as methods of curing epoxy resins.
U.S. Pat. Nos. 4,879,414 and 4,927,902 relate to certain polythiol curing agents for epoxy resins prepared by the reaction of hydrogen sulfide or organic dithiols with polyglycidyl substituted amines. Exemplified curing agents have aromatic, methylene, bis-diphenyl, xylylene, cycloaliphatic, methylene bis-dicylohexyl, dimethylene cyclohexyl, methylene cyclohexyl or aliphatic cores with one or more thiol-substituted amine groups:—N(CH2CHOHCH2SX)2 where X is H or R′—SH, where R′ is alkylene, cycloalkylene or alkylene substituted aromatic. The cured resins are reported to exhibit improved cured rates, better heat resistance, greater resistance to chemicals and greater resistance to water absorption. Each of these references is incorporated by reference herein in its entirety for descriptions of epoxy resins, certain useful polythiol curing agents as well as additives and methods of curing epoxy resins and applications of cured epoxy resins.
U.S. Pat. No. 4,626,562 relates to an epoxy resin composition consisting essentially of an epoxy compound having at least two epoxy groups in each molecule, certain esters of a mercaptoalkylcarboxylic acid and a tertiary amine-type curing accelerator. Certain polyol esters of mercaptoalkylcarboxylic are exemplified, such as triesters of trimethylolpropane. The epoxy composition is reported to be useful in construction and for repairs to asphalt concrete or cement concrete. This reference is incorporated by reference herein in its entirety for descriptions of epoxy resins, certain useful polythiol curing agents, catalysts and additives as well as methods of curing epoxy resins and applications of cured epoxies.
U.S. Pat. No. 5,972,423 relates to use of a curable filler composition including an epoxy compound, a polythiol and a catalyst for repairing substrate surfaces without need for application of a primer.
U.S. Pat. No. 6,153,719 relates to a composition useful as a sealer comprising certain epoxy compounds, a thiol curing agent, a catalyst and a phosphorous-containing compound having an ethylenically unsaturated group which is described as an adhesion-promoting compound. Each of these references is incorporated by reference herein for descriptions of epoxy resin materials that can be cured using polythiols, for descriptions of certain polythiol curing agents, useful catalysts and additives as well as for descriptions of methods of curing epoxies and applications of such epoxies.
U.S. Pat. No. 5,430,112 relates to epoxy resin compositions which contain certain epoxy resins, a polythiol and certain accelerators which are reported to exhibit curability at relatively low heating temperature and a long working life. Accelerators include a solid-dispersion-type amine adduct latent curing accelerator or an accelerator which is prepared by reaction of certain isocyanate compounds with certain primary of secondary amines. U.S. Pat. No. 5,214,098 relates to a hardenable mixture comprising an epoxide resin, a certain latent epoxide resin hardener, a certain amine and a certain thiol. U.S. Pat. No. 6,872,762 relates to a curable epoxy-based composition having an epoxy compound, a latent hardener, at least one solid organic acid and optionally a polythiol. Each of these references is incorporated by reference herein for descriptions of epoxy resin materials that can be cured using polythiols, for descriptions of certain polythiol curing agents and useful catalysts and particularly for useful latent catalysts (or accelerators) as well as for descriptions of additives and of methods of curing epoxies and applications of such epoxies.
U.S. Pat. No. 4,177,173 relates to polyepoxide curing employing a curing system having at least one polymercaptan and at least one catalyst which is a poly[(N,N-dimethylamino) alkyl ether. The combination of polymercaptan (polythiol) and poly amine catalyst is reported to provide rapid and effective curing. This patent reports that the pot life of thiol-cured epoxies can be extended as much as ten times by using a tertiary amine-ether catalyst alone or in combination with a traditional tertiary amine with no sacrifice in the cure rate once it commences (i.e. a sharp gel point is maintained). This reference is incorporated by reference herein in its entirety for descriptions of polyepoxies (epoxy resins), certain useful polythiol curing agents and particularly for certain useful amine catalysts (tertiary amine-ethers) for description of useful additives, as well as for method of curing epoxies.
Jones and coworkers report the use of certain tris(mercaptoalkyl)cyclohexanes as curing agents for epoxy resins (U.S. Pat. Nos. 3,505,166 and 3,624,160). The patents specifically report 1,2,4-tris(2-mercaptoethyl) cyclohexane and 1,3,5-tris(2-mercaptoethyl) cyclohexane.
Hickner et al. report the compositions of certain cycloaliphatic polythiols and their use as curing agents for polyepoxides (U.S. Pat. Nos. 3,873,502 and 3,828,100). The patent reports cycloaliphatic polythiols of formula:
where R is —Cl, —Br, —SR1SH or —OR2SR1SH and at least two R have a terminal thiol group, and R1 is an alkylene group of 2 to 10 carbons having one or more —O— or —S— ether groups and R2 is an alkylene group of 2-4 carbon atoms. Each of these patents is incorporated by reference herein for its description of cycloaliphatic polythiols including specific compounds of the listed formula.
Hiroshi reports an epoxy adhesive wherein the composition contains a triazinethiol containing at least one mercapto group (e.g. 1,3,5-trimercaptotriazine) (JP5093179(A), 1993).
U.S. published application 2010/0273940 relates to thiol curing agents for epoxy resins which is reported to have favorable pot life, good storage stability and where the cured product has good water resistance. The curing agent is described as containing a secondary or tertiary branched thiol compound having a substituent on a carbon atom at the alpha-position to a thiol group. Exemplified substituents on the alpha carbon are straight chain or branched alkyl groups. Specifically exemplified curing agents have formula:X(—O—CO—(CR1R2)n—CR3R4—SH)m wherein n is an integer from 0 to 4 and m is an integer from 2 to 8, X is “an m valent aliphatic or aromatic residue of at most 20 carbon atoms which may have a substituent” and where R1-R4 are independently hydrogen, or an alkyl group having 1-10 carbon atoms and at least one of R3 or R4 is an alkyl group having 1-10 carbon atoms.
Burns (WO 2012059558 A1, 2011) teaches the use of polythiols having at least one secondary or tertiary thiol group per molecule; and a stabilizing component comprising a solid organic acid.
Kazuo (EP 2597047 A1), Nakano (U.S. Pat. No. 8,420,738 B2) and Ozawa (U.S. Pat. No. 6,492,454 B1) teach certain bismercaptotriazines as vulcanizing agents for rubbers with structure:
wherein M is H, Li, Na, K, ½ Mg, ½ Ca, ½ Ba and R is SH, OR1, SR2, NHR3, NR4R5 and R1, R2, R3, R4 and R5 are alkyl, alkenyl, aryl, aralkyl, alkylaryl, or cycloalkyl.